It’s no secret that a walk in the woods makes us feel great -- especially this time of year when much of Canada is a riot of colour of changing leaves. But what is it exactly about strolling through green space that restores us?

It could be the mere act of walking; after all, any physical activity gets our blood pumping and the oxygen flowing. But lots of studies have shown that a brisk walk in the city is nowhere near as relaxing to both the mind and the body as a walk in nature.

Is it the sounds of the birds? The sight of trees and vegetation? The fresh air?

New research suggests it’s all those things and they have one common denominator: they enhance the functioning of our immune systems.

University of Illinois environment and behaviour researcher Ming Kuo has been studying nature’s effect on health. She’s combed through dozens of studies that have demonstrated the specific ways that walks in nature improve our health. They include:

reducing blood glucose

reducing inflammation

improving sleep by promoting relaxation

increasing feelings of awe and gratitude

restoring attention

But Kuo believes the main way that nature works its magic on us is by helping us switch from “fight or flight” mode (which kicks in when we're stressed), to a more restorative “rest and digest” mode.

When we’re in “rest and digest,” we feel safe and our bodies can relax. That allows our bodies to invest resources toward such things as digestion, cell renewal and restoration of the immune system.

“When we feel completely safe, our body devotes resources to long-term investments that lead to good health outcomes—growing, reproducing, and building the immune system,” Kuo said recently in a statement.

Now of course, there are lots of indoor ways to find relaxation, such as with yoga, mindfulness meditation, or listening to music. But Kuo says nature provides “active ingredients” that can improve our health. These include:

phytoncides, which are antimicrobial volatile organic compounds that plants give off and that can reduce blood pressure and boost immune functioning

negative air ions found in the air in forested and mountainous areas and near moving water, which reduce depression

mycobacterium vaccae, a common soil bacterium that has been shown to work as an antidepressant

nature sounds, which studies have shown activate the parasympathetic system and reduce heart rate

and of course sunshine, which causes our bodies to produce vitamin D.

Kuo believes that all these ingredients of nature combine to enhance our immune systems.

“Nature doesn’t just have one or two active ingredients. It’s more like a multivitamin that provides us with all sorts of the nutrients we need,” she said